CONTINUOUS MONITORING OF THE HYDRATION OF PORTLAND CEMENT AT EARLY AGES

The early age hydration of Portland cement paste and mortar was continuously monitored by measuring the ultrasound velocity and the dielectric constant. The experimental results show that the ultrasound velocity and the dielectric constant are clearly affected by the hydration of cement paste. They are closely related to the distribution and volume fractions of solid, liquid and gas phases in the materials. The hydration process of Portland cement at early ages is divided into five stages, namely the dormant period, acceleration, deceleration, final setting and stabilization period. The change rate of the ultrasound velocity is mainly influenced by the hydration degree of cement. The higher hydration degrees result in larger ultrasound velocities. The dielectric constant of Portland cement mortar decreases with increasing hydration ages, and is linearly related to the ultrasound velocity of cement paste with the same water to cement ratio.